ZCS uses SpamAssassin to control spam. SpamAssassin uses predefined rules as well as a Bayes database to score messages. Zimbra evaulates spaminess based on percentage. Messages tagged between 33%-75% are considered spam and delivered to the user’s junk folder. Messages tagged above 75% are not sent to the user and are discarded.

When zmtrainsa runs, these messages are used to teach the spam filter. Make sure you add a large enough sampling of messages to get accurate scores. To determine whether to mark messages as spam at least 200 known spams and 200 known hams must be identified.

The postfix_policy_time_limit key is set because by default the Postfix spawn (8) daemon kills its child process after 1000 seconds. This is too short for a policy daemon that might run as long as an SMTP client is connected to an SMTP process.